1. Field of the Invention
The present invention relates to a thermal printer.
2. Description of the Related Art
A thermal printer that includes a thermal print part including a thermal head and a platen roller is widely adopted as an attached printer attached to a cash register, a portable terminal device, an ATM (Automated Teller Machine) and the like.
In this kind of thermal printer, a clamshell type thermal printer has an apparatus main body including a frame and an access cover that respectively include modules, and functions as a printer by allowing the modules to be combined in a state of the access cover being closed.
In such a clamshell type printer, for example, a configuration is known where the frame of the apparatus main body and the access cover respectively include a thermal head and a platen roller, and the access cover is fixed by allowing a bearing of the platen roller to be supported by the frame of the main body in a state of the access cover being closed.
According to such a configuration, because the platen roller is attached to the access cover, the platen roller is detached from the main body with the access cover when the access cover is opened, which makes it possible to exchange a print paper sheet and remove a paper jam readily and quickly.
In a conventional example, FIG. 1 is a perspective view showing a main part including a frame that supports a platen roller 51 of a thermal printer 200.
A frame of the thermal printer 200 of the conventional example is made up of a main body 100 and side plates 101 and 102, and further includes a paper guide part 103, a gear case 104 and the like. The main body 100 and the side plates 101 and 102 of the frame are an integral part made of zinc and the like formed by die-casting. The paper guide part 103 and the gear case 104 are molded articles made of resin material, and fitted into the main body 100 or the side plates 101 and 102.
The frame includes a thermal head not shown in the drawing, a head spring 53 to press the thermal head to the platen roller 51, a motor 21 to drive and rotate the platen roller 51 and the like, and detachably supports bearings 5 and 7 of the platen roller 51 by platen roller receiving parts 105 and 106.
The platen roller 51 is, for example, mounted on an access cover not shown in the drawing, with its bearings 5 and 7 inserted into the platen roller receiving parts 106 and 105 of the side plates 101 and 102 of the frame, respectively, and is fixed and supported by a platen roller holding spring 9 at a predetermined force.
FIG. 2 is a main part side view seen from the side plate 102 of the thermal printer 200 of the conventional example. FIG. 2 shows a state of the bearing 7 of the platen roller 51 inserted into the platen roller receiving part 105 of the side plate 102 and fixed by the platen roller holding spring 9.
The platen roller holding spring 9 includes a holding part 9a of the bearing 7 of the platen roller 51 and a curved part 9b fitted to a convex part 10 provided on the side plate 102. The platen roller holding spring 9 is formed by bending a wire spring made of a metal and the like.
Because the platen roller holding spring 9 can bend in a direction opposite to the axis of the platen roller 51, the platen roller holding spring 9 makes possible attaching and detaching the bearing 7 of the platen roller 51, and fixes and supports the bearing 7 at a certain force when the bearing 7 has been inserted in the platen roller receiving part 105.
The thermal printer 200 of the conventional example makes possible attaching and detaching the platen roller 51 by using the platen roller holding spring 9 as mentioned above. However, because the conventional thermal printer 200 requires the wire spring, a number of parts and labor hours for bending the wire spring and attaching the bended wire spring to the side plate 102 increase, which causes an increase of cost.
FIGS. 3A through 3C are views showing a configuration of the thermal printer 200 including bearings and a gear of the platen roller 51 in the conventional example. FIG. 3A is a plan view of the platen roller 51 to which the bearings 5 and 7, the gear 4, and a washer 6 are attached. FIG. 3B is an exploded perspective view of the respective parts. FIG. 3C is an enlarged view of a shaft part of the platen roller 51 to which the bearing 7 and the washer 6 are attached.
As shown in FIGS. 3A and 3B, the platen roller of the conventional example includes the gear 4 and the bearing 5 on one end, and the bearing 7 and the washer 6 on the other end, and is made up of five parts as a whole.
The bearing 5 is inserted into the platen roller receiving part 106 of the side plate 101 of the frame of the thermal printer 200 shown in FIG. 1, and the bearing 7 is inserted into the platen roller receiving part 105 of the side plate 102 as well, by which the platen roller 51 is fixed and supported rotatably.
As shown in FIGS. 3A and 3B, the bearings 5 and 7 are respectively mounted on shaft ends 11b and 11c, and are provided to allow the shaft to spin free inside. A shaft end 11a of the platen roller 51 having a D-cut shape in cross-section perpendicular to the axial direction of the platen roller 51 is pressed into the gear 4, which drives to rotate the platen roller 51 by receiving a drive force of a motor 21 (which is shown in FIG. 1) through a reduction gear. As shown in FIG. 3C, the bearing 7 is fixed by the washer 6 not to come out after being mounted on the shaft 11c of the platen roller 51.
In the thermal printer 200 of the conventional example, the frame that supports the bearings 5 and 7 of the platen roller 51 is formed by die-casting of zinc and the like, and the platen roller holding spring 9 to press the bearings 5 and 7 is formed of the wire spring of a metal material.
Accordingly, if the bearings 5 and 7 are configured to rotate with the revolving platen roller 51, the bearings 5 and 7 are worn away between the platen roller receiving parts 105 and 106, and the platen roller holding spring 9. Hence, the bearings 5 and 7 are required to be fixed and supported by the platen roller parts 105 and 106, and are not to be rotated by the platen roller 51 revolving with the gear 4, which results in increasing a number of parts needed.
FIGS. 4A through 4C show side views of the platen roller 51 and the gear 4 of the conventional example. FIG. 4A is a side view of the platen roller 51. FIG. 4B is a side view of the gear 4. FIG. 4C is a side view of the gear 4 mounted on the shaft 11a of the platen roller 51.
As shown in FIG. 4A, in an end of the shaft 11a that is inserted into the gear 4 of the platen roller 51, a flat part 12 is formed so that the cross-section perpendicular to the axial direction has a D-cut shape. Moreover, as shown in FIG. 4B, the gear 4 includes a press fit hole 13 that has a flat part 13a and a D-cut shape slightly smaller than the cross-section of the shaft 11a of the platen roller 51, and the shaft lie of the platen roller 51 is pressed into the press fit hole 13.
In order to fit the shaft 11 of the platen roller 51 into the gear 4 with only the flat part 12 for driving rotation, because there is a concern that the shaft 11a may idle if the flat part 12 in cross-section of the shaft end 11a is too small, the flat part 12 is required to be a certain size.
Furthermore, in order to press the shaft end 11a having the formed flat part 12 into the press fit hole 13 of the gear 4 and to fix the shaft more certainly, the press fit hole 13 also needs the flat part 13a corresponding to the flat part 12 of the shaft end lie of the platen roller 51.
As shown in FIG. 4C, when the shaft 11a of the platen roller 51 is pressed into the gear 4, the gear 4 and the shaft end 11a of the platen roller 51 are fixed at the D-cut surface (i.e., flat part) 12. If the gear 4 is rotated, a force from the gear 4 is transmitted to the ends of the D-cut surface 12, which is shown by dotted lines in the drawing, formed into the shaft end 11a of the platen roller 51.
Here, in pressing the shaft end 11a of the platen roller 51 into the gear 4, because the shaft end 11a is pressed into the gear 4 after the respective flat parts 12 and 13a of the shaft 11a of the platen roller 51 and the press fit hole 13 of the gear 4 are adjusted to become flat by visual observation using a jig, so that assembly requires a certain number of labor hours.
As mentioned above, the thermal printer 200 requires parts such as the wire spring and the like to support the bearings 5 and 7 of the platen roller 51. In addition, the bearings 5 and 7 that contact the side plates 101 and 102 of the frame made of a metal material must be configured not to be rotated with the platen roller 51, which causes an increase in the numbers of parts and labor hours for production.
For example, Japanese Patent Application Laid-Open Publication No. 2011-56691 discloses a related art example.